Bar Soap Compositions Containing Zinc Pyrithione And A Metal-Pyridine Oxide Complex

ABSTRACT

The present invention relates to a bar soap composition that contains zinc pyrithione (ZPT) and a metal-pyridine oxide complex, preferably a zinc-pyridine oxide complex. The bar soap may be characterized by enhanced discoloration resistance, extended shelf life, and/or increased anti-microbial efficacy.

FIELD OF THE INVENTION

The present invention relates to personal cleansing compositions, morespecifically bar soap compositions, comprising zinc pyrithione and ametal-pyridine oxide complex with enhanced discoloration resistance,extended shelf life, and/or increased anti-microbial efficacy.

BACKGROUND OF THE INVENTION

Pyrithione (also known as 1-Hydroxy-2-pyridinethione,2-pyridinethiol-1-oxide, 2-mercaptopyridine-N-oxide,pyridine-2-thione-N-oxide, pyridinethione-N-oxide, 2-pyridinethione,pyridinethione, or simply “PT”) has been noted for its bactericidal andfungicidal activities. Pyrithione is a bidentate ligand that formsstable complexes with most transitional metals. Metallization ofpyrithione often results in highly augmented biocidial activities. Metalsalts of pyrithione, such as for example, sodium pyrithione, magnesiumpyrithione, barium pyrithione, bismuth pyrithione, strontium pyrithione,copper pyrithione, zinc pyrithione, cadmium pyrithione, and zirconiumpyrithione, are widely used as fungicides and bactericides in a broadspectrum of commercial products, such as metalworking fluids,lubricants, paints, cosmetics and toiletries.

Zinc pyrithione (or “ZPT”) is especially useful as a broad-spectrumanti-microbial agent and preservative. It is active against bothgram-positive and gram-negative bacteria, as well as fungi and yeasts.Therefore, ZPT has been used in various personal care compositions, suchas for example, anti-dandruff shampoos, hair conditioners, leave-ontonics, and anti-microbial foot powders.

Bar soap is a popular product form for cleansing. A bar soap comprisingZPT is particularly desirable for its broad-spectrum anti-microbialefficacy. Aesthetics of consumer products such as bar soaps havesignificant impact on the consumers' perception of the products, whichwill in turn determine the acceptability of the products by theconsumers. However, pyrithione-containing compounds can becomediscolored in the presence of ferric or cupric ions, even if the ferricirons are present only in trace amounts. The metal ions can also beintroduced into the soap compositions unintentionally as impurities inthe raw materials used for making bar soap. Further, duringmanufacturing, handling or storage, various metallic parts of themanufacturing equipment, such as for example, roller mills, pipes, ornozzles, may come into contact with the soap noodles or pellets, therebyintroducing metal ions into the soap composition. In some situation,such contact can be maintained for a long time (e.g. overnight to 24hours), and at a relatively elevated temperature, thereby increasinginteraction between ZPT and metal ions. The resultant discoloration mayadversely affect the overall aesthetics of the bar soaps and giveconsumers a negative impression of the soap quality.

In the past, a number of solutions have been developed in attempt tosolve the ZPT discoloration problem. For example, in U.S. Pat. No.4,161,526, JP Patent Publication 2001-278863A, U.S. Pat. No. 4,482,715,U.S. Pat. No. 4,957,658 and U.S. Pat. No. 4,818,436, a number ofmaterials including zinc-containing materials, borates, reducing agents(such as alkali metal sulfites, alkali metal bisulfites, hydrazine andthe like), and HEDP have been used to address the ZPT discolorationproblem. However, none of these solutions can completely eliminate oreffectively reduce the undesirable discoloration in ZPT-containing barsoaps, which remains a continuing concern for manufacturers.

There is a continuing need for improved ZPT-based anti-microbial barsoaps with better color stability or enhanced resistance againstdevelopment of discoloration.

Further, ZPT has been known to be unstable when solubilized. It mayundergo transformation upon exposure to oxidizing species or certaintransition metals, such as copper and iron. The anti-microbial effect ofZPT-based personal care compositions can therefore diminishsubstantially over time in environments susceptible to oxidation ormetallization. Therefore, there is also a need for ZPT-basedanti-microbial personal cleansing compositions with improved andextended shelf life or enhanced anti-microbial efficacy.

SUMMARY OF THE INVENTION

The present invention relates to a personal cleansing compositioncontaining: (a) ZPT, (b) particles of a metal-pyridine oxide complex,which comprises a pyridine oxide compound coordinately bound to metalions, and (c) at least one surfactant. Such a personal cleansingcomposition is preferably in the form of a bar soap and characterized bya pH value ranging from about 10 to about 10.7 when dispersed in a 1 wt% aqueous solution

In another aspect, the present invention relates to a method for forminga bar soap, which includes the steps of: (a) preparing a mixturecontaining about 0.01% to about 5% of ZPT, from about 0.01% to about 10%of particles of the above-described metal-pyridine oxide complex, andfrom about 20% to about 95% of at least one surfactant by total weightof said mixture; and (b) shaping the mixture to form a bar soap. The barsoap so formed preferably has a pH value ranging from about 10 to about10.7 when dispersed in a 1 wt % aqueous solution.

In an embodiment, the metal in the metal-pyridine oxide complex may beselected from the group consisting of iron, copper and zinc. In apreferred but non-limiting embodiment of the present invention, theparticles of Zn-pyridine oxide complex are pre-formed by combining apyridine oxide compound with zinc oxide or a soluble zinc salt and thenmixed with ZPT and the surfactant. In an alternative embodiment, suchparticles of Zn-pyridine oxide complex are formed in situ by directlycombining the pyridine oxide compound, zinc oxide or a soluble zincsalt, ZPT and the surfactant.

These and other aspects of the present invention will become moreapparent upon reading the following drawings and detailed description ofthe invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing the bacteria reduction rates of various soapcompositions that respectively contain 0.5% ZPT alone, 0.5% Zn—HPNOcomplex alone, and combinations of ZPT and Zn—HPNO complex at variousconcentrations (e.g., 0.1%, 0.25% and 0.5%) against a gram-positivebacteria, Staphylococcus aureus (S. aureus), as measured by the pigskinResidual Efficacy Test (RET) test.

DETAILED DESCRIPTION OF THE INVENTION

“Bar soaps” as used herein refers to solid or semi-solid articles forwashing, bathing, and cleaning that contain either soap surfactants,synthetic surfactants, or mixtures thereof (i.e., semi-synthetics) asdescribed hereinafter. A bar soap as used herein is not limited to a barshape but can have any regular or irregular shape, including but notlimited to: cubic, rectangular, spherical, oval, cylindrical, pyramidaland the like. The bar soaps of the present invention are preferably, butnot necessarily, characterized by a volume ranging from 1 cm³ to 1,000cm³, more preferably from 10 cm³ to 500 cm³, and most preferably from 50cm³ to 200 cm³, and a weight ranging from 0.5 g to 5 Kg, more preferablyfrom 1 g to 1 Kg, and most preferably from 10 g to 500 g.

Except as otherwise noted, the articles “a”, “an”, and “the” mean “oneor more.” The term “comprising” means that other steps and otheringredients which do not affect the end result can be added, and thisterm encompasses the terms “consisting of” and “consisting essentiallyof”. The compositions and methods/processes of the present invention cancomprise, consist of, and consist essentially of the essential elementsand limitations of the invention described herein, as well as any of theadditional or optional ingredients, components, steps, or limitationsdescribed herein. Particularly, the compositions of the presentinvention contain ZPT, at least one acidic pH adjusting agent, and atleast one soap surfactant as the essential ingredients, and they maycontain one or more additional or optional ingredients as describedhereinafter.

All percentages, parts and ratios are based upon the total weight of thepersonal cleansing compositions of the present invention, unlessotherwise specified. All such weights as they pertain to listedingredients are based on the active level and, therefore do not includecarriers or by-products that may be included in commercially availablematerials.

All ratios are weight ratios unless specifically stated otherwise. Alltemperatures are in Celsius degrees, unless specifically statedotherwise.

As used herein, the term “effective” means an amount of a subject activehigh enough to provide a significantly positive modification of thecondition to be treated. An effective amount of the subject active willvary with the particular condition being treated, the severity of thecondition, the duration of the treatment, the nature of concurrenttreatment, and like factors.

In one aspect, the present invention relates to a bar soap compositioncomprising the combination of ZPT and particles of a metal-pyridineoxide complex and has an overall pH value ranging from 9.9 to 10.7 whendispersed in a 1 wt % aqueous solution. Such a bar soap compositionexhibits enhanced color stability or discoloration resistance,particularly in the presence of high concentration of ferric or cupricions.

In an embodiment, the metal in the metal-pyridine oxide complex isselected from the group consisting of iron, copper and zinc. However, itwill be understood by one skilled in the art that other metals can beselected according to the Irving Williams Series. Without wishing to bebound by any particular theory, it is believed that the presence ofparticles of a Zn-pyridine oxide complex in a bar soap composition of pH9.9 to 10.7 is particularly effective in inhibiting or retardingtranschelation between dissolved pyrithione (PT) ions and ferric orcupric ions and formation of colored precipitates, thereby eliminatingor significantly reducing discoloration. In addition, the existence ofsuch a Zn-pyridine oxide complex leads to a visible change of color inany precipitate actually formed, i.e., from a black/blue/green hue to amore visually acceptable red/orange hue. Such red/orange hue is unlikelyto have adverse impact on the consumer's acceptability of the bar soapproduct.

Further, bar soap compositions containing the combination of ZPT andZn-pyridine oxide complex within the scope of the present inventionexhibit substantially extended shelf life by stabilizing ZPT againstpotential environmental assaults. This technical effect is bothsurprising and unexpected, especially in light of the fact that additionof uncomplexed pyridine oxide compound into the bar soap compositionscontaining ZPT not only fails to stabilize ZPT but in fact attributes toits further deterioration.

Still further, the combination of ZPT with Zn-pyridine oxide complexresults in a synergistic enhancement of antimicrobial efficacy againstgram-positive bacteria, such as Staphylococcus aureus (S. aureus).

Although bar soap is the preferred product form for carrying thecombination of ZPT and Zn-pyridine oxide complex, the scope of thepresent invention is not thus limited. Instead, the present inventionmay also encompass other product forms of rinse-off personal cleansingcompositions, which include but not are limited to: body washes, showergels, liquid hand soaps, shampoos, conditioners, facial cleansers, andthe like.

Zinc Pyrithione (ZPT)

Zinc pyrithione (ZPT) is incorporated in the personal cleansingcompositions of the present invention in the form of a combination, amixture, a dispersion, a suspension, or an emulsion. Preferably, but notnecessarily, ZPT is present in a spherical or platelet form, while theZPT particles have an average size of up to about 20 microns, morepreferably up to about 10 microns, even more preferably up to about 5microns, and most preferably up to about 2.5 microns. Alternatively, ZPTis present in a particulate form that is non-platelet and non-spherical,having a configuration selected from the group consisting of rods,needles, cylinders, cones, ellipsoids, prisms, parallelepipeds,pyramids, tetrahedrons, hexahedrons, octahedrons, dodecahedrons,icosahedrons, and combinations thereof, as described by U.S. Pat. No.6,242,007.

In a preferred embodiment of the present invention, the ZPT included inthe bar soap composition is a dry powder ZPT in platelet particle form(“platelet ZPT”). Such platelet ZPT can have a median particle diameterof, for example, from about 0.05 to about 10 microns, alternatively fromabout 0.1 to about 8 microns, and alternatively from about 0.2 to about5 microns, and alternatively about 3 microns. The platelet ZPT can alsohave a thickness of, for example, from about 0.1 to about 15 microns,alternatively from about 0.5 to about 1 micron, alternatively from about0.6 to about 0.8 microns, and alternatively from about 0.6 to about 0.7microns, as described in U.S. Patent Publication 2012/0219610.

ZPT as used in the present invention may be made by reacting1-hydroxy-2-pyridinethione (i.e., pyrithione acid) or a soluble saltthereof with a zinc salt (e.g., ZnSO₄) to form a ZPT precipitate, asillustrated by the disclosures of U.S. Pat. No. 2,809,971, or processedinto platelet ZPT using, for example, sonic energy as illustrated byU.S. Pat. No. 6,682,724, or by any other methods currently known in theart. While higher concentrations of ZPT have been observed to controlthe growth of a wider range of micro-organisms, the useful amount of ZPTthat can be added to a commercial product is limited by efficacy andeconomic considerations, regulatory restrictions, and environmentalconcerns. In personal cleansing compositions, such as soaps, the amountof ZPT that may be added is further limited by toxicological concerns.Preferably, but not necessarily, the bar soap compositions of thepresent invention contains ZPT in the amount ranging from about 0.01% toabout 5% by total weight of such compositions. More preferably, suchcompositions contains from about 0.1% to about 2.0% ZPT by total weight.

Particles of Metal-Pyridine Oxide Complex

The personal cleansing compositions of the present invention furthercomprise a metal-pyridine oxide complex, which comprises a pyridineoxide compound that is coordinately bound to a metal ion. In anembodiment, the metal is selected from the group consisting of iron,copper and zinc. However, it will be understood by one skilled in theart that other metals can be selected according to the Irving WiliamsSeries, which refers to the relative stability of complexes formed by ametal ion. In a preferred embodiment, the metal is zinc. Suchzinc-pyridine oxide complex has a surprising and unexpected effect onthe discoloration resistance of the ZPT-containing bar soapcompositions, which is demonstrated by a significant increase in itsresistance to laboratory-induced discoloration in comparison withcontrol samples containing ZPT only. Without wishing to be bound bytheory, according to Iriving Williams Series, a more stable complex canbe formed between pyrithione and metal ions having smaller ionic radius.For example, Fe³⁺ has a radius of 0.64 A, which is smaller than Cu²⁺which has a radius of 0.73 A, and which is in turn smaller than that ofZn²⁺ 0.74A. Thus, this might help to explain why you have pyrithionediscoloration in ZPT-containing bar soaps in the presence of othertransition metal sources (e.g., copper and iron).

According to this embodiment, the zinc-pyridine oxide complex acts insynergy with ZPT to improve the anti-microbial effect of the personalcleansing compositions, especially against gram-positive bacteria. Itmay further provide an extended shelf life for such anti-microbialpersonal cleansing compositions.

In a particularly preferred embodiment of the present invention, thepyridine oxide compound has the following chemical structure:

wherein R₁, R₂, R₃, R₄, and R₅ are each independently selected from thegroup consisting of H, OH, a halogen (such as F, Cl, Br, and I), NO,NO₂, and a C₁-C₁₂ organic group that is linear or branched, saturated orunsaturated, substituted or unsubstituted.

More preferably, R₁ or R₅ is OH, and R₂, R₃, and R₄ is eachindependently selected from the group consisting of H, OH, and a C₁-C₈alkyl, alkylene, alkyne, or aryl group. It is to be understood thatvarious potential and actual resonate structures of the pyridine oxidesmay exist (i.e., the bond between the N and O atoms and/or the bondbetween the neighboring C atom and —OH group may resonate between asingle bond and a double bond), for example, as follows:

It is intended that all of the reasonable resonate structures are meantto be represented by the formula (I) hereinabove and are therebyincluded within the scope of the present invention.

Useful pyridine oxide compounds that can be employed in the practice ofthe present invention include 2-hydroxypyridine-N-oxide (“HPNO”),N-hydroxy-6-octyloxy-2(1H)-pyridone, ciclopirox olamine, piroctoneolamine, and derivatives thereof.

A representative species of pyridine oxide compounds that isparticularly useful for the practice of the present invention is2-hydroxypyridine-N-oxide (“HPNO”), which has the chemical structure of:

As a bidentate chelant, HPNO is capable of forming coordinationcomplexes with transition metal ions in solution. Specifically, two HNPOcan be bound to one zinc ion to form a Zn—HNPO complex with thefollowing structure:

Zn—HPNO is a particularly preferred Zn-pyridine oxide compound for thepresent invention. It is important to note that zinc ions can formvarious complexes with HPNO, with one, two, three, or even four HPNOattached to one zinc ion, although only the complex with two HPNOattached to one zinc ion as shown by formula (III) has a neutral charge.In solution, zinc ions and HPNO may undergo speciation to form a mixtureof different complex species, and the relative concentration of suchcomplex species can vary depending on the chemical environment they arein, such as pH and the presence of other metal ions or chelant species.For ease of reference, all such complex species are herein referred toas the “Zn—HPNO complex,” regardless of the actual number of HPNOincluded, and they are all included within the scope of the presentinvention.

Various derivatives or salts of HPNO with similar chemical structure canalso form similar complexes with Zn ions and are therefore also usefulfor the practice of the present invention. Exemplary HPNO derivatives orsalts include, but are not limited to: 6-hydroxy-3-pyridine sulfonicacid, 1-oxide (CAS 191672-18-1); 2-hydroxy-4-pyridine carboxylic acid,1-oxide (CAS 13602-64-7); 5-ethoxy-2-pyridinol, 2-acetate, 1-oxide (CAS51984-49-7); 1-(3-hydroxy-2-oxido-4-isoquinolinyl)-ethanone (CAS65417-65-4); 6-hydroxy-3-pyridine carboxylic acid, 1-oxide (CAS90037-89-1); 2-methoxy-4-quinolinecarbonitrile, 1-oxide (CAS379722-76-6); 2-pyridine carboxylic acid, 6-hydroxy-, 1-oxide (CAS1094194-45-2); 3-pyridine carboxylic acid, 2-hydroxy-, 1-oxide (CAS408538-43-2); 2-pyridinol, 3-nitro-, 1-oxide (CAS 282102-08-3);3-pyridine propanenitrile, 2-hydroxy-, 1-oxide (193605-60-6); 3-pyridineethanol, 2-hydroxy-, 3-acetate, 1-oxide (CAS 193605-56-0); 2-pyridinol,4-bromo-, 1-oxide (CAS 170875-41-9); 2-pyridinol, 4,6-dibromo-,2-acetate, 1-oxide (CAS 170875-40-8); 2-pyridinol, 4,6-dibromo, 1-oxide(CAS 170875-38-4); 2-pyridinol, 4-(2-aminoethyl)-, 1-oxide (CAS154403-93-7); 2-pyridinol, 5-(2-aminoethyl)-, 1-oxide (CAS 154403-92-6);3-pyridine propanoic acid, α-amino-6-hydroxy-, 1-oxide (CAS134419-61-7); 2-pyridinol, 3,5-dimethyl, 1-oxide (CAS 102074-62-4);2-pyridinol, 3-methyl-, 1-oxide (CAS 99969-07-0); 2-pyridinol,3,5-dinitro, 1-oxide (CAS 98136-47-1); 2-pyridinol, 3,5-dibromo-,1-oxide (CAS 98136-29-9); 2-pyridinol, 4-methyl-6-(2-methylpropyl)-,1-oxide (CAS 91408-77-4); 2-pyridinol, 3-bromo-4,6-dimethyl-, 1-oxide(CAS 91408-76-3); 2-pyridinol, 4,5,6-trimethyl-, 1-oxide (CAS91408-75-2); 2-pyridinol, 6-heptyl-4-methyl-, 1-oxide (CAS 91408-73-0);2-pyridinol, 6-(cyclohexylmethyl)-4-methyl-, 1-oxide (CAS 91408-72-9);2-pyridinol, 6-bromo-, 1-oxide (CAS 89284-00-4); 2-pyridinol, 5-bromo-,1-oxide (CAS 89283-99-8); 2-pyridinol, 3,5-dichloro-4,6-difluoro-,1-oxide (CAS 33693-37-7); 2-pyridinol, 3,4,5,6-tetrachloro-, 1-oxide(CAS 32835-63-5); 2-pyridinol, 6-methyl-, 1-oxide (CAS 14420-62-3);2-pyridinol, 5-nitro-, 1-oxide (CAS 14396-03-3); 2-pyridinol,4-methyl-5-nitro-, 1-oxide (CAS 13602-77-2); 2-pyridinol,4-chloro-5-nitro-, 1-oxide (CAS 13602-73-8); 2-pyridinol, 4-chloro-,1-oxide (CAS 13602-65-8); 2-pyridinol, 4-nitro-, 1-oxide (CAS13602-63-6); and 2-pyridinol, 4-methyl-, 1-oxide (CAS 1952-64-3), andmixtures thereof. These compounds are commercially available from, forexample, Sigma-Aldrich (St. Louis, Mo.) and/or Aces Pharma (Branford,Conn.).

The amount of zinc-pyridine oxide complex present in the bar soapcompositions of the present invention may range from about 0.01% toabout 10% by total weight of such compositions. More preferably, suchcompositions contains from about 0.05% to about 7% zinc-pyridine oxidecomplex, still more preferably from about 0.1% to about 7% or from about0.5% to about 5%, or most preferably from about 1% to about 3% by totalweight.

The zinc-pyridine oxide complex as used in the present invention ispresent in the compositions as particles, which can be pre-formed byreacting the pyridine oxide compound with a soluble zinc salt, such asZnSO₄, ZnCl₂, or a mixture thereof, thereby forming an insolubleprecipitate. The term “soluble” as used herein refers to a solubility ofat least 0.01 gram per liter in an aqueous solution at 25° C. Theprecipitate is then processed into dry powders or used to form acolloidal or slurry composition containing particulates dispersed in asolution, which can be subsequently added into the personal cleansingcompositions.

Alternatively, the particles of zinc-pyridine oxide complex can beformed in situ by directly adding the precursors, i.e., the pyridineoxide compound and the soluble zinc salt, into the personal cleansingcompositions, which will complex with each other in the compositions toform particles. The pyridine oxide compound and zinc salt can be addedeither in dry power form or pre-dissolved in a solution.

The particles of zinc-pyridine oxide complex are characterized by anaverage particle size ranging from about 0.05 micron to about 5,000microns, preferably from about 0.1 micron to about 2,000 microns, morepreferably from about 0.2 micron to about 1,000 microns, and mostpreferably from about 1 micron to about 600 microns.

The particle size of the zinc-pyridine oxide complex can be readilycontrolled by modulating the homogenization rate when mixing the solublezinc salt and the pyridine oxide compound, i.e., the faster thehomogenization, the slower the particle growth rate, and consequentlythe smaller the particles. The particles can further be processed bymilling or grinding to achieve a more uniform particle sizedistribution.

The molar ratio of ZPT to Zn-pyridine oxide complex in the personalcleansing compositions of the present invention is preferably rangingfrom about 5:1 to about 1:10, more preferably from about 2:1 to about1:5, still more preferably from about 1:1 to about 1:3, and mostpreferably about 1:1.5 to about 1:2.

PH and PH Adjusting Agents

When the personal cleansing compositions of the present invention are inform of bar soaps, they are preferably characterized by a pH valueranging from 9.9 to 10.7 when dispersed in a 1 wt % aqueous solution.More preferably, the bar soap compositions have a pH range of 10.1 to10.6, and most preferably from 10.2 to 10.5. This pH range isparticularly beneficial for maintaining the dissolution equilibrium ofZPT and the Zn-pyridine oxide complex in the soap compositions, and canthereby extend or maximize the shelf life of the bar soaps.

The pH of the personal cleansing compositions of the present inventioncan be readily adjusted or modulated by various mechanisms. In onespecific embodiment of the present invention, the pH modulation isachieved through employment of an acidic pH adjusting agent. Any acidsuitable for use in personal cleansing formulation, e.g., either aninorganic acid or an organic acid, can be employed in the practice ofthe present invention. Examples of inorganic acid suitable for practiceof the present invention include, but are not limited to: hydrochloricacid, sulfuric acid, sulphurous acid, nitric acid, nitrous acid,phosphoric acid, boric acid, and the like. Suitable organic acidsinclude carboxylic acids, sulfonic acids and fatty acids.

Fatty acids are particularly preferred acidic pH adjusting agents forthe practice of the present invention. Any fatty acids with total carbonnumbers ranging from C₆ to C₂₄ can be used for the practice of thepresent invention. Exemplary fatty acids include, but are not limitedto: caproic acid, caprylic acid, capric acid, lauric acid, myristicacid, palmitic acid, stearic acid, arachidic acid, behenic acid,lignoceric acid, cerotic acid, myristoleic acid, palmitoleic acid,sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid,linoelaidic acid, a-linolenic acid, arachidonic acid, eicosapentaenoicacid, erucic acid, docosahexaenoic acid, and the like. Particularlyuseful fatty acids for the practice of the present invention aresaturated or unsaturated fatty acids with total carbon numbers rangingfrom C₁₂ to C₂₂, such as, for example, lauric acid, myristic acid,palmitic acid, stearic acid, palmitoleic acid, oleic acid, and behenicacid.

In an alternative embodiment of the present invention, the pH modulationcan be achieved by adjusting the amounts of raw materials used forsoap-making, i.e., fats, oils, and base materials such as sodium orpotassium hydroxide, so as to reach a final personal cleansingcomposition with the desired pH value. In yet another alternativeembodiment of the present invention, the pH modulation can be achievedusing a pH buffering agent, such as potassium carbonate or zinccarbonate.

Reducing Agents

The personal cleansing compositions of the present invention mayoptionally comprise one or more reducing agents, which are preferably,but not necessarily, selected from sterically hindered phenols. Suchreducing agents can further improve the discoloration resistance of thesoap compositions as well as extending the shelf life thereof.

Sterically hindered phenolic reducing agents suitable for the use of thepresent invention are characterized by a molecular weight above 500 Da.Preferred examples include 2,4-dimethyl-6-octyl-phenol;2,6-di-t-butyl-4-methyl phenol (i.e., butylated hydroxy toluene);2,6-di-t-butyl-4-ethyl phenol; 2,6-di-t-butyl-4-n-butyl phenol;2,2′-methylenebis(4-methyl-6-t-butyl phenol);2,2′-methylenebis(4-ethyl-6-t-butyl phenol); 2,4-dimethyl-6-t-butylphenol; 4-hydroxymethyl-2,6-di-t-butyl phenol;n-octadecyl-beta(3,5-di-t-butyl-4-hydroxyphenyl)propionate;2,6-dioctadecyl-4-methyl phenol; 2,4,6-trimethyl phenol;2,4,6-triisopropyl phenol; 2,4,6-tri-t-butyl phenol;2-t-butyl-4,6-dimethyl phenol; 2,6-methyl-4-didodecyl phenol;tris(3,5-di-t-butyl-4-hydroxy isocyanurate, andtris(2-methyl-4-hydroxy-5-t-butylphenyl)butane.

More preferred are pentaerythrityl tetra-di-t-butylhydroxyhydrocinnamate (Tinoguard® TT, BASF);octadecyl-3,5-di-t-butyl-4-hydroxy-hydrocinnamate (NAUGARD 76, UniroyalChemical; IRGANOX 1076, Ciba-Geigy);tetrakis+methylene(3,5-di-t-butyl-4-hydroxy-hydrocinnamate)}methane(NAUGARD 10, Uniroyal Chemical; IRGANOX 1010, Ciba-Geigy); 2,2′-oxamidobis+ethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)}propionate (NAUGARD XL-1,Uniroyal Chemical); 1,2-bis(3,5-di-t-butyl-4-hydroxyhydrocinnamoy 0hydrazine (IRGANOX MD 1024,Ciba-Geigy);1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)-s-triazine-2,4,6(1H,3H,5H)trione (IRGANOX 3114,Ciba-Geigy);1,3,5-tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)-s-triazine-2,4,6-(1H,3H,5H)trione(CYANOX 1790, American Cyanamid Co.);1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene(ETHANOX 330, Ethyl Corp.); 3,5-di-t-butyl-4-hydroxyhydrocinnamic acidtriester with1,3,5-tris(2-hydroxyethyl)-5-triazine-2,4,6(1H,3H,5H)-trione, andbis(3,3-bis(4-hydroxy-3-t-butylphenyl)butanoic acid)glycolester.

Most preferred reducing agents for the practice of the present inventionare pentaerythrityl tetra-di-t-butyl hydroxyhydrocinnamate, which iscommercially available under the trade name of Tinogard® TT from BASF(Monheim, Germany).

The amount of reducing agent present in the personal cleansingcompositions of the present invention may range from about 0.001% toabout 5% by total weight of such compositions. More preferably, suchcompositions contains from about 0.01% to about 1% of the reducingagent, and most preferably from about 0.02% to about 0.5%, by totalweight of such compositions.

Soap Surfactants

The bar soap of the present invention will typically comprise a soapsurfactant, or in short “soap”, in an amount ranging from about 40%,45%, 50% to about 65%, 75%, 84%. The term “soap” is used herein in itspopular sense, i.e., the alkali metal or alkanol ammonium salts ofalkane- or alkene monocarboxylic acids. Sodium, magnesium, potassium,calcium, mono-, di- and tri-ethanol ammonium cations, or combinationsthereof are suitable for purposes of the present invention. In general,sodium soaps are used in the compositions of this invention, but fromabout 1% to about 25% of the soap may be ammonium, potassium, magnesium,calcium or a mixture of these soaps. The soaps useful herein are thewell known alkali metal salts of alkanoic or alkenoic acids having about12 to 22 carbon atoms, preferably about 12 to about 18 carbon atoms.They may also be described as alkali metal carboxylates of alkyl oralkene hydrocarbons having about 12 to about 22 carbon atoms.

It can be preferred to use soaps having the fatty acid distribution oftallow and vegetable oil (i.e., “fatty acid soaps”). More preferably,the vegetable oil is selected from the group consisting of peanut oil,rapeseed oil, corn oil, olive oil, palm oil, coconut oil, palm kerneloil, palm oil stearine, and hydrogenated rice bran oil, or mixturesthereof, since these are among the more readily available fats.Especially preferred are palm oil stearine, palm kernel oil, and/orcoconut oil. The proportion of fatty acids having at least 12 carbonatoms in coconut oil soap is about 85%. This proportion will be greaterwhen mixtures of coconut oil and fats such as tallow, palm oil, ornon-tropical nut oils or fats are used, wherein the principal chainlengths are C₁₆ and higher. A preferred soap is sodium soap having amixture of about 50% tallow, 30% palm oil stearine, and 20% palm kerneloil or coconut oil.

Soaps may be made by the classic kettle boiling process or moderncontinuous soap manufacturing processes wherein natural fats and oilssuch as tallow or coconut oil or their equivalents are saponified withan alkali metal hydroxide using procedures well known to those skilledin the art. Alternatively, the soaps may be made by neutralizing fattyacids, such as lauric (C₁₂), myristic (C₁₄), palmitic (C₁₆), or stearic(C₁₈) acids with an alkali metal hydroxide or carbonate.

Synthetic Surfactants

Synthetic surfactants can be utilized in the present bar soapcompositions, either in combination with or in place of the soapsurfactants described hereinabove, to further improve the latheringproperties of the bar soap during use. When a majority of thesurfactants in the bar soap compositions of the present invention aresynthetic surfactants rather than soap surfactants, the pH value of thebar soap compositions can be readily broaden to the relatively lower pHrange of 7-9. In certain embodiments, the pH value of such bar soapcompositions may approach the neutral pH range of 6-8, which isparticularly beneficial because the resulting bar soaps are more gentleand less irritating to the skin.

The synthetic surfactants useful in this invention include anionic,amphoteric, nonionic, zwitterionic, and cationic surfactants. Syntheticsurfactants are typically incorporated in the present compositions at alevel of from about 0.1% to about 20%, preferably from about 0.5% toabout 10%, and more preferably from about 0.75% to about 5%, by weightof the composition.

Examples of anionic surfactants include but are not limited to alkylsulfates, anionic acyl sarcosinates, methyl acyl taurates, N-acylglutamates, acyl isethionates, alkyl ether sulfates, alkylsulfosuccinates, alkyl phosphate esters, ethoxylated alkyl phosphateesters, trideceth sulfates, protein condensates, mixtures of ethoxylatedalkyl sulfates and the like. Alkyl chains for these surfactants areC₈-C₂₂, preferably C₁₀-C₁₈ and, more preferably, C₁₂-C₁₄ alkyls.

Zwitterionic surfactants can be exemplified by those which can bebroadly described as derivatives of aliphatic quaternary ammonium,phosphonium, and sulfonium compounds, in which the aliphatic radicalscan be straight chain or branched and wherein one of the aliphaticsubstituents contains from about 8 to 18 carbon atoms and one containsan anionic water-solubilizing group, for example, carboxy, sulfonate,sulfate, phosphate, or phosphonate. Examples include:4-[N,N-di(2-hydroxyethyl)-N-octadecylammonio]-butane-1-carboxylate;5-[S-3-hydroxypropyl-S-hexadecylsulfonio]-3 hydroxypentane-1-sulfate;3-[P,P-P-diethyl-P3,6,9trioxatetradecyl-phosphonio]-2-hydroxypropane-1-phosphate;3-[N,N-dipropyl-N-3-dodecoxy-2-hydroxypropylammonio]-propane-1-phosphonate;3-(N,N-di-methyl-N-hexadecylammonio)propane-1-sulfonate;3-(N,N-dimethyl-N-hexadecylammonio)-2-hydroxypropane-1-sulfonate;4-(N,N-di(2-hydroxyethyl)-N-(2hydroxydodecyl)ammonio]-butane-1-carboxylate;3-[S-ethyl-S-(3-dodecoxy-2-hydroxypropyl)sulfonio]-propane-1-phosphate;3-(P,P-dimethyl-P-dodecylphosphonio)-propane-1-phosphonate; and5-[N,N-di(3-hydroxypropyl)-N-hexadecylammonio]-2-hydroxy-pentane-1-sulfate.

Examples of amphoteric surfactants which can be used in the compositionsof the present invention are those which can be broadly described asderivatives of aliphatic secondary and tertiary amines in which thealiphatic radical can be straight chain or branched and wherein one ofthe aliphatic substituents contains from about 8 to about 18 carbonatoms and one contains an anionic water solubilizing group, e.g.,carboxy, sulfonate, sulfate, phosphate, or phosphonate. Examples ofcompounds falling within this definition are sodium3-dodecylaminopropionate, sodium 3-dodecylaminopropane sulfonate;N-alkyltaurines, such as the one prepared by reacting dodecylamine withsodium isethionate according to the teaching of U.S. Pat. No. 2,658,072;N-higher alkyl aspartic acids, such as those produced according to theteaching of U.S. Pat. No. 2,438,091; and the products sold under thetrade name “Miranol” and described in U.S. Pat. No. 2,528,378. Otheramphoterics such as betaines are also useful in the present composition.Examples of betaines useful herein include the high alkyl betaines suchas coco dimethyl carboxymethyl betaine, lauryl dimethyl carboxy-methylbetaine, lauryl dimethyl alpha-carboxyethyl betaine, cetyl dimethylcarboxymethyl betaine, lauryl bis-(2-hydroxyethyl)carboxy methylbetaine, stearyl bis-(2-hydroxypropyl)carboxymethyl betaine, oleyldimethyl gamma-carboxypropyl betaine, laurylbis-(2-hydro-xypropyl)alpha-carboxyet-hyl betaine, etc. Thesulfobetaines may be represented by coco dimethyl sulfopropyl betaine,stearyl dimethyl sulfopropyl betaine, amido betaines,amidosulfobetaines, and the like.

Examples of suitable cationic surfactants include stearyldimenthylbenzylammonium chloride; dodecyltrimethylammonium chloride;nonylbenzylethyldimethyl ammonium nitrate; tetradecylpyridinium bromide;laurylpyridinium chloride; cetylpyridinium chloride; laurylpyridiniumchloride; laurylisoquinolium bromide; ditallow(Hydrogenated)dimethylammonium chloride; dilauryldimethyl ammonium chloride; and stearalkoniumchloride; and other cationic surfactants known in the art.

Nonionic surfactants useful in this invention can be broadly defined ascompounds produced by the condensation of alkylene oxide groups(hydrophilic in nature) with an organic hydrophobic compound, which maybe aliphatic or alkyl aromatic in nature.

A preferred synthetic surfactant for use in the present compositions issodium laureth-3 sulfate. Sodium laureth sulfate tends to provideexcellent lathering properties, especially when combined with sodiumtripolyphosphate as the inorganic salt in the present compositions.

Other Ingredients

The personal cleansing compositions of the present application canadditionally comprise inorganic salts (especially inorganic zinc salts,such as zinc carbonate, zinc sulfate, zinc nitrate, zinc fluoride, zincchloride, zinc borate, and the like as well as zinc oxide), structurants(such as raw starch, pregelatinzed starch, carboxymethyl cellulose,polyacrylate polymer, Carbopol, carregeenan, xanthan gum, polyethyleneglycol, polyethylene oxide, and the like), free fatty acids (such asthose derived from tallow, coconut, palm and palm kernel), humectants,cationic polymers (such as cationic polysaccharides, cationicpolyalkylene imines, cationic hydroxyethyl cellulose, and the like),brighteners, fillers (such as silica, talc, and the like), perfumes,sequestering agents, coloring agents, opacifiers and pearlizers (such astitanium dioxide).

All of these are useful in enhancing the appearance, smell or othercosmetic/sensory properties of the product.

In a particularly preferred embodiment of the present invention, thepersonal cleansing compositions contain zinc carbonate at an amountranging from about 0.01% to about 5%, more preferably from about 0.1% toabout 3%, and most preferably from about 1% to about 2% by total weightof the composition Zinc carbonate provided at such an amount isparticularly effective in reducing or removing malodor.

As bar soaps, the appearance of the personal cleansing compositions ofthe present invention can be transparent, translucent, or opaque, andthe color thereof can be white, off-white, cream, yellow, pink, red,green, purple, blue and black. In one embodiment, the bar soapcomposition is opaque with a white or off-white color.

Preparation Methods

Bar soap compositions of the present invention can be made via a numberof different processes known in the art. Preferably, the presentcompositions are made via a milling process, resulting in milled barsoap compositions. A typical milling process of manufacturing a bar soapcomposition includes: (a) a step in which the soap is made througheither a continuous process (ConSap or continuous saponificationprocess) or a batch-making process (i.e. neutralization process forhydrolysis fatty acid noodle or kettle process), (b) a vacuum dryingstep in which the soap is made into soap noodles, (c) an amalgamatingstep in which the soap noodles are combined with other ingredients ofthe bar soap composition, (d) a milling step in which a relativelyhomogeneous mixture is obtained, (e) a plodding step in which the soapmixture is extruded as soap logs and then cut into soap plugs, and (f) astamping step in which the soap plugs are stamped to yield the finishedbar soap composition. The present bar soap can be made using any of theabove mentioned manufacturing processes, and the ZPT, the Zn-pyridineoxide complex (or the precursors for in situ forming such complex), andpH adjusting agent, and the reducing agent can be added during themixing steps of preparing the bar soaps.

Other product forms of the present invention, such as body washes,shower gels, liquid hand soaps, shampoos, facial cleansers, and thelike, can be readily formed by the conventional mixing or homogenizationprocess.

Clinical Benefits

The personal cleansing compositions of the present invention havedemonstrated various clinical benefits, which include but are notlimited to: anti-microbial, de-germing, anti-dandruff, efficacy againstatopic dermatitis, odor control, and the like.

Discoloration Test

As used herein, “discoloration” means the color change brought byformation of colored precipitates from a reaction between ZPT andunwanted metal ions, such as ferric ions and/or cupric ions. Thediscoloration can be in a color of grayish blue, blue, black, purple,green, and the like, which is different from the original color of acomposition comprising ZPT. By “original color”, it means the color ofthe composition before ZPT in the bar soap has an opportunity to reactwith ferric and/or cupric ions. For ease of measurement and comparison,discoloration in bar soaps herein is artificially induced by addingsolutions containing ferric and/or cupric ions, and the color differencein the bar soaps before and after the artificial introduction of ferricand/or cupric ions is measured quantitatively using a colormeter orother well known equipment.

Specifically, once sample bar soaps are ready to be tested fordiscoloration resistance or the lack thereof, a circular surface areawith a diameter of 23.50 mm is marked on the surface of each bar soap.Such a circular surface perfectly matches the diameter of a probe in aGretag-Macbeth™ Color-Eye 3100 colormeter, which is employed in thepresent invention to measure the color LAB values of the sample barsoaps before any discoloration was induced by introduction of ferricions (“Standard Color”).

Subsequently, 60 μL of freshly prepared FeCl₃ solution containing 0.023wt % of FeCl₃ is titrated onto the marked circular surface area tointentionally induce discoloration. After being placed under roomtemperature out of direct light exposure for 2 hours, various degrees ofdiscoloration will develop on the top layer of the sample bar soapwithin the marked circular surface area where the FeCl₃ solution istitrated.

The marked circular surface area is then analyzed by the Gretag-Macbeth™Color-Eye 3100 colormeter to determine the LAB color values of thediscoloration induced by addition of the FeCl₃ solution (“SampleColor”).

The colors are hereby quantified by the well-known LAB values.Specifically, the L value represents the lightness or brightness of thecolor measured, i.e., the higher the L value, the lighter or brighterthe color. The A value represents the redness/greenness of the colormeasured, with positive A values stand for red colors and negative Avalues stand for green colors. The B value represents theyellowness/blueness of the color measured, with positive B values standfor yellow colors and negative B values stand for blue colors. Whencomparing the difference between a Sample Color and a Standard color, apositive Delta L (ΔL), which is calculated as =L_(Sample)−L_(Standard),indicates that the Sample Color is lighter than the Standard Color, anda negative ΔL indicates that the Sample Color is darker than theStandard Color. A positive Delta A (ΔA), which is calculated as=A_(Sample)−A_(Standard), indicates that the Sample Color is redder, anda negative ΔA indicates that the Sample Color is green. A positive DeltaB (ΔB), which is calculated as =B_(Sample)−B_(Standard), indicates thatthe Sample Color is yellower, and a negative ΔB indicates that theSample Color is bluer.

ZPT Stability

As mentioned hereinabove, ZPT may undergo transformation upon exposureto oxidizing species, thereby losing its anti-microbial effect over timein environments susceptible to oxidation. Such vulnerability of ZPT toenvironmental assaults is well known in the art, and various solutionshave been proposed to stabilize ZPT with limited success.

It is a surprising and unexpected discovery of the present inventionthat the above-described Zn-pyridine oxide complex is effective instabilizing ZPT in bar soap compositions and reducing ZPT loss even inharsh chemical environments.

The chemical stability of ZPT is evaluated by an aging test described asfollows, so as to determine the percentage loss of ZPT after such agingtest. First, a bar soap containing ZPT is obtained, preferablyimmediately after it is manufactured. The starting content of ZPT insuch bar soap (in percentage) is measured by method describedhereinafter using a portion of the bar soap, or a companion bar madefrom the same batch of soap noodle. The bar soap is weighed (+/−0.01 g),and its starting weight is recorded. Second, the bar soap is subjectedto an aging process, during which the bar soap is placed inside a sealedwater impermeable bag, which is preferably made of polyethylene (PE).The bag containing the bar soap is then left either at room temperature(i.e., about 25° C.), or in a convection oven at an elevated temperature(e.g., 50° C.), for an extended period (e.g., 10 days, 12 days, 14 days,or up to 36 months in certain cases). After the aging, if placed in aconvection oven at the elevated temperature, the bar soap is taken outof the convection oven and allowed to return to room temperature (i.e.,25° C.). The bar soap is weighed again, and its final weight isrecorded. The final content of ZPT in the bar soap (in percentage) ismeasured by the same method as described hereinafter.

Chemical stability of the ZPT is calculated by the following equation toobtain the percentage loss of ZPT:

${{\% \mspace{14mu} {Loss}\mspace{14mu} {of}\mspace{14mu} {ZPT}} = {\left\lbrack {1 - \frac{\begin{matrix}{{Final}\mspace{14mu} {Bar}\mspace{14mu} {Weight} \times} \\{{Final}\mspace{14mu} {ZPT}\mspace{14mu} {Content}\mspace{14mu} (\%)}\end{matrix}}{\begin{matrix}{{Starting}\mspace{14mu} {Bar}\mspace{14mu} {Weight} \times} \\{{Starting}\mspace{14mu} {ZPT}\mspace{14mu} {Content}\mspace{14mu} (\%)}\end{matrix}}} \right\rbrack \times 100\%}},$

The content of ZPT in bar soap compositions is measured herein by aniodine-based titration method, which is described in greater detail inthe following sections. The mercapto group in zinc pyrithione can betitrated by iodine, which oxidizes it to the disulfide-2,2′dithiobispyridine-1-oxide. If ZPT has already been oxidized or undergonetransformation otherwise so that it no longer possesses the mercaptogroup, it will not be detectible by the iodine-based titration methoddescribed hereinafter.

First, a standardized 0.04N iodine solution is prepared. Specifically,anhydrous sodium thiosulphate (with a minimum purity of 99%) isoven-dried for 2 hours at 105° C. and then stored in a dessicator. 0.05grams (+/−0.0001 g) of the anhydrous sodium thiosulfate is weighed andplaced into the 100 mL polypropylene beaker of an autotitrator, and 50mL of deionized water is added to form a standard solution. Theautotitrator used herein is preferably a Mettler DL25 or MettlerDM140-SC titrator with platinum ring electrode, which is commerciallyavailable from Mettler Toledo Internantional, Inc. (Switzerland), or anequivalent thereof. The autitrator is set up to titrate the standardsodium thiosulfate solution with the iodine solution that is beingstandardized. Bubbles are eliminated from the burette of theautotitrator, and titration is commenced. Such procedure is repeatedtwice more, and the results are averaged to obtain a standardized 0.04Niodine solution. The % relative standard deviation (RSD) should be lessthan 1% of the average.

Next, standardized 0.01N and 0.006N iodine solutions are prepared.Specifically, standardized 0.01N iodine solution is prepared using 0.10g (+/−0.0001 g) sodium thiosulphate dissolved in 100 mL deionized water,using 10.0 mL pipetted into the 100 mL autotitrator breaker with 50 mLadditional deionized water followed by the titration procedure.Standardized 0.006N iodine solution is prepared using 3.0 mL of a 0.01Msodium thiosulphate solution and 40 mL of a solvent (containing 13% v/vhydrochloric acid in 6% v/v butanol), followed by addition of 40 mL of1:1 hexane/isopropanol. The autotitration procedure is subsequentlycarried out. The iodine solutions are standardized daily.

The bar soap whose ZPT content is to be measured is then shredded usinga grater and stirred to form a homogenous mixture. 4.00 grams of theshredded soap is weighed and put into a clean, dry beaker of anautotitrator. 75 mL of hot 6% v/v butanol (which was heated in aboiling-water bath) and 5 mL of concentrated HCl (provided at roomtemperature) are then added into the beaker. The mixture is agitatedvigorously so as to fully dissolve all soluble components. The beaker issubsequently placed in the autotitrator, and bubbles are completelyeliminated from the burette.

The titration is then initiated and analyzed while the mixture is stillwarm. The mixture is vigorously agitated during the titration procedure.For compositions with less than 0.2% of ZPT by weight, titration iscarried out using the 0.006N iodine solution. For compositions withhigher ZPT concentrations, the initial starting sample weight can bereduced. Titration can be done either manually or by using autotitrationprocedure by those with skill in the art.

The ZPT content in the bar soap is calculated as follows:

${{{ZPT}\mspace{14mu} {Content}\mspace{14mu} (\%)} = \frac{{Volume}\mspace{14mu} {of}\mspace{14mu} {Iodine}\mspace{14mu} {Solution}\mspace{14mu} ({ml}) \times N \times 15.88\%}{{Sample}\mspace{14mu} {Weight}\mspace{14mu} (g)}},$

wherein N is the normality of the standardized iodine solution, andwherein 15.88% is a constant that is derived from:

$\begin{matrix}{{15.88\%} = \frac{{Molecular}\mspace{14mu} {Weight}\mspace{14mu} {of}\mspace{14mu} {ZPT} \times 100\%}{{Number}\mspace{14mu} {of}\mspace{14mu} {Pyrithione}\mspace{14mu} {per}\mspace{14mu} {Molecule} \times 1000\mspace{14mu} {ml}\text{/}{Liter}}} \\{{= \frac{371.6 \times 100\%}{2 \times 1000\mspace{14mu} {ml}\text{/}{Liter}}},}\end{matrix}$

The above-described procedure is repeated three times for each bar soapcomposition whose ZPT content is to be measured, and the results areaveraged to obtain a final ZPT content in percentage (%) for thespecific bar soap. All chemical reagents employed hereinabove arehigh-purity reagents obtained from VWR Scientific (Batavia, Ill., USA)or other scientific chemical suppliers.

PH Measurement

The pH value of a bar soap composition is measured in aqueous solutionat about 25° C., and it can be measured using any commercially availablepH meter calibrated with pH standard solutions, such as, for example,the SevenMulti™ pH meter available from Mettler Toledo International,Inc. (Switzerland). Specifically, a bar soap composition whose pH valueis to be measured is first dissolved in distilled water at aconcentration of 1 wt % and a temperature of 35° C. by agitationprovided by a magnetic stir bar in a sealed container for one hour. Thesoap solution is then cooled to about 25° C. (+/−0.2° C.), and the pH ismeasured. The pH of the 1 wt % aqueous solution is then recorded as thepH of the bar soap composition.

Water Activity

Water Activity (“Aw”) is a measurement of the energy status of the waterin a system. It indicates how tightly water is bound, structurally orchemically, within a composition. Water activity (“Aw”) is defined asthe ratio of the water vapor pressure over a sample (P) to that overpure water (P_(o)):

$A_{W} = \frac{P}{P_{0}}$

Water activity of a bar soap composition can be measured electronicallyusing a water activity meter with a sealed chamber and an electrical oroptical measurement of the headspace. The meter is calibrated against aseries of saturated salt solutions. A bar soap composition to bemeasured is placed in the chamber held at ambient temperature which isthen allowed to equilibrate with the headspace in the chamber. Atequilibrium, the relative humidity of the air in the chamber is the sameas the water activity of the composition.

For purposes of the present invention, the water activity (Aw) of a barsoap composition can be measured using a Hygrolab 3 Water Activity Meteravailable from Rotronic, Inc. (Huntington, N.Y., USA). The followingprocedure is employed to determine the water activity (Aw) of a bar soapcomposition:

-   -   1. Check the chamber of the meter to make sure it is clean and        dry before the test;    -   2. Cut a bar soap into pieces of about 0.2-0.4 cm thick with a        stainless steel knife;    -   3. Put the soap pieces into a clean, dry plastic sample        container with a depth of ½″;    -   4. Press the soap pieces with a gloved finger lightly to make        sure that the bottom of the container is covered by the soap        pieces;    -   5. Put the sample container back into the chamber of the meter        and cover it with the chamber top, which contains the electronic        headspace measurement apparatus;    -   6. Wait for the headspace to reach equilibrium (approximately        1-2 hours); and    -   7. Record the temperature and the Aw value.

Preferably, but not necessarily, the bar soap compositions of thepresent invention are characterized by a water activity of less than0.9, more preferably between about 0.4 and 0.9, still more preferablybetween 0.5 and 0.9, and most preferably between 0.6 and 0.9. The barsoap can be manufactured with a water activity of about 0.85, and duringdistribution, such bar soap can dehydrate to obtain a lower wateractivity of between 0.5 and 0.8, or between 0.55 and 0.75, or between0.6 and 0.75.

EXAMPLES Example 1 Pre-Formation of Zinc-HPNO Complex

Particles of Zn—HPNO complex can be pre-formed using the following rawmaterials:

TABLE I Raw Materials Nominal (w/w %) Actual Amount (g) HPNO* 11.1055.50 NaOH (solid)** 4.00 20.00 Water 1 (DI) 40.00 200.00 ZnSO₄•7H₂O***14.35 71.75 Water 2 (DI) 30.55 152.75 Total 100.00 500.00 *Commerciallyavailable from Suzhou Highfine Biotech Co., Ltd. **Analytical gradeavailable from Tianjin Jiaxin Chemicals Glass Instrument Trading Co.,Ltd. ***Analytical grade available from Tianjin Jiaxin Chemicals GlassInstrument Trading Co., Ltd.

The following procedure can be followed to pre-form the Zn—HNPO complexof the present invention:

-   -   Pre-weigh 200 grams of the deionized (DI) water, i.e., DI water        1;    -   Add 20 grams of NaOH into the DI water;    -   Use a magnetic bar to stir up a vortex so as to dissolve the        NaOH completely;    -   Add 55.5 grams of HPNO into the mixture;    -   Use the magnetic bar to stir up a vortex so as to dissolve the        HPNO until the solution turns yellowish transparent;    -   Pre-weigh 152.75 grams of the DI water, i.e., DI water 2, and        place it in a separate container;    -   Add 71.75 grams of ZnSO₄.7H₂O into DI water 2;    -   Use a magnetic bar to stir up a vortex so as to dissolve the        ZnSO₄.7H₂O completely;    -   Add the ZnSO₄ solution into the HPNO solution slowly while        continuing to use the magnetic bar to stir, so as to avoid        formation of any large precipitation;    -   Maintain the vortex by adjust the agitation speed as necessary        and continue the agitation for more than 30 minutes after all        the ZnSO₄ solution is added into the HPNO solution;    -   Formation Zn—HPNO precipitate in the mixture can be observed;    -   Let the resulting mixture sit for 1 hour;    -   Carefully pour out the supernatant of the mixture;    -   Wash the precipitant 2-3 times using DI water;    -   Transfer the precipitant slurry to a centrifuge tube and spin at        15,000 rpm for 30 minutes;    -   Pour out the supernatant again;    -   Transfer the resulting paste to under a ventilation hood and        allow it to dry at room temperature;    -   The air-dried paste contains about 35% water, and the Zn—HNPO        complex is 65% active therein; and    -   The dried powder can be further milled as necessary.

Example 2 In Situ Formation of Zinc-Pyridine Oxide Complex

A HPNO solution is first prepared by using the following raw materials:

TABLE II Raw Materials Amount (w/w %) HPNO 22.20 NaOH (Active, 100%)8.00 Water (DI) 69.80 Total 100.00

The following steps can be followed to form Zn—HNPO complex in situ:

-   -   Pre-weigh required amount of DI water;    -   Add NaOH into the DI water while gradually stirring with a        magnetic bar until the mixture is transparent;    -   Add the required amount of HNPO into the mixture while        continuing to stir with the magnetic bar until the final mixture        turns transparent yellow; and    -   The HPNO solution and ZnSO₄.7H₂O powder are then introduced into        soap noodles into amalgamator separately with other ingredients        (such as perfumes, colorants, fillers, and the like) without        being pre-mixed, followed by the standard soap-making processing        steps such as mixing, milling, and extruding to form soap bars.

Example 3 Comparative Discoloration Test

Four different bar soaps A-D were prepared containing ingredients aslisted in Table III below. Specifically, Comparative example A (i.e.,the control) contained soap noodle only without any ZPT or Zn—HPNOcomplex. Comparative example B contained soap noodle with ZPT butwithout Zn—HPNO complex. Sample C contained soap noodle with ZPT incombination of pre-formed particles of Zn—HPNO complex. Sample Dcontained soap noodle with ZPT in combination with HPNO and ZnSO4, whichreacted with each other in situ to form the Zn—HPNO complex.

TABLE III Comparative Comparative Ingredient (wt %) Example A Example BExample C Example D Soap Noodle* 76.60 80.48 75.81 75.84 ZPT — 0.20 0.200.20 Pre-formed Zn-HPNO complex — — 0.60 — HPNO (65% active) — — — 0.64ZnSO₄•7H₂O — — — 0.18 Pentaerythrityl tetra-di-t-butyl 0.00 0.03 0.030.03 hydroxyhydrocinnamate** TiO2 0.40 0.40 0.40 0.40 Starch 17.00 17.0017.00 17.00 Perfume 1.00 1.00 1.00 1.00 Brightener-49 0.02 0.02 0.020.02 Water Q.S. Q.S. Q.S. Q.S. *The soap noodle contained the followingingredients:

indicates data missing or illegible when filed

TABLE IV Ingredients Wt % Sodium palmate (from palm oil and palm oil49.683 sterine) Sodium tallowate (from tallow) 16.027 Sodium palmkernelate (from palm kernel oil) 14.424 Unsaponifiable matter 0.540Citric acid (anhydrous) 0.100 Sodium citrate 0.152 Pentasodium pentetate0.050 Tetrasodum etidronate 0.050 Sodium chloride (low sodium) 0.553Glycerine 3.471 Coconut acid 0.950 Water Q.S. ** Commercially availableas Tinogard TT from BASF (Monheim, Germany).

Following are quantitative measurements of color changes in LAB valuesthat were observed in the bar soaps before and after the addition of theFeCl₃ solution, following the procedure of the Discoloration Testdescribed hereinabove:

TABLE V Delta L Delta A Delta B Comparative Example A −0.462 0.117 0.542Comparative Example B −8.377 2.165 −4.653 Example C −6.5 0.682 11.298Example D −7.257 1.464 12.87

The data shown in Table V hereinabove indicates that the ComparativeExample A (i.e., control), which contains no ZPT, underwent very littlecolor change before and after the addition of FeCl₃, while theComparative Example B, which contained 0.2% ZPT without the Zn—HPNOcomplex, exhibited significant color change and more specifically,significant blue discoloration, as indicated by the negative ΔB value.In comparison, Example C and D that contained either pre-formed or insitu formed particles of Zn—HPNO complex exhibited highly positive ΔBvalues, which indicated that the color change migrated from the bluespectrum to the yellow spectrum, and that the undesirable bluediscoloration was effectively eliminated by introduction of the Zn—HPNOcomplex.

Example 4 Comparative ZPT Stability Test

A. ZPT only Vs. ZPT+ZnSO₄

A first comparative experiment was carried out to assess the percentageloss of ZPT in bar soap compositions containing ZPT alone in comparisonwith compositions containing ZPT in combination with ZnSO₄. Thefollowing two bar soap compositions were prepared:

TABLE VI Amount (w/w %) Comparative Comparative Raw Materials Example EExample F Dry Soap Noodle 76.68 76.68 TiO2 0.40 0.40 Starch 17.00 17.00ZPT (48% active) 0.42 0.42 ZnSO4•7H2O — 5.00 (7.78% solution) Perfume1.00 1.00 Brightener 49 0.02 0.02 DI water Q.S. Q.S.

The pH values, initial weights and initial ZPT contents in the bar soapsof Comparative Examples E and F were measured according to theprocedures described hereinabove. The bar soaps were then subjected toenvironment stresses in an incubator at 50° C. with 60% humidity for 12days, after which the final weights and final ZPT contents werere-measured and used to calculate the loss of ZPT. The measurementsresults are as follows:

TABLE VII Comparative Comparative Results Example E Example F pH (1%solution) 10.42 10.36 Initial ZPT Content (w/w %) 0.201 0.206 Final ZPTContent (w/w %) 0.199 0.188 Initial Bar Weight (g) 42.06 43.81 Final BarWeight (g) 40.08 43.39 ZPT Loss (%) 5.66 9.61

The above comparative examples demonstrate that in the presence ofZnSO₄, ZPT in a bar soap composition is actually less stable than inthat contained only ZPT.

B. ZPT only Vs. ZPT+Zn—HNPO

A second comparative experiment was carried out to assess the percentageloss of ZPT in bar soap compositions containing ZPT alone in comparisonwith compositions containing ZPT in combination with Zn—HPNO complex.The following two bar soap compositions were prepared:

TABLE VIII Amount (w/w %) Comparative Inventive Raw Materials Example GExample H Soap Noodle 76.18 78.23 TiO2 0.40 0.40 Starch 17.00 17.00 ZPT(48% active) 0.42 0.42 Pre-formed Zn-HNPO — 0.60 particles (65% active)*Perfume 1.00 1.00 Pentaerythrityl tetra-di- 0.05 0.05 t-butylhydroxyhydrocinnamate Brightener 49 0.02 0.02 DI water Q.S. Q.S. *Formedfollowing the procedures described in Example I here in above.

The pH values, initial weights and initial ZPT contents in the bar soapsof the Comparative Example G and the Inventive Example H were measuredaccording to the procedures described hereinabove. The bar soaps werethen subjected to environment stresses in an incubator at 50° C. with60% humidity for 12 days, after which the final weights and final ZPTcontents were re-measured and used to calculate the loss of ZPT. Themeasurement results are as follows:

TABLE IX Comparative Inventive Results Example G Example H pH (1%solution) 10.36 10.32 Initial ZPT Content (w/w %) 0.202 0.205 Final ZPTContent (w/w %) 0.192 0.201 Initial Bar Weight (g) 43.62 43.44 Final BarWeight (g) 42.13 42.51 ZPT Loss (%) 8.20 4.05

The above examples demonstrated that in the presence of Zn—HPNO complex,ZPT in a bar soap composition is more stable than in that contained onlyZPT.

C. ZPT+HNPO Vs. ZPT+Zn—HPNO

A third comparative experiment was carried out to assess the percentageloss of ZPT in bar soap compositions containing ZPT in combination withuncomplexed HPNO as compared with compositions containing ZPT incombination with Zn—HPNO complex. The following two bar soapcompositions were prepared:

TABLE X Amount (w/w %) Comparative Inventive Raw Materials Example IExample J Soap Noodle 98.10 98.10 ZPT (48% active) 0.42 0.42 Zn-HNPOpremix 0.00 1.48 (HPNO concentration = 20.2%) HPNO Solution 1.48 0.00(20.2% active) Perfume 1.00 1.00 Process Moisture loss 1.00 1.00

The Zn—HPNO premix was prepared by mixing a HPNO solution with a ZnCl₂solution in the experiment, with a HPNO concentration of 20.2% and aZnCl₂ concentration of 12.74%. The preparation procedures followedprocedures as described hereinabove except without centrifugation. Themixture was continuously stirred to make sure that it was homogenousbefore addition into the soap noodle.

ZPT contents of the Comparative Example I and the Inventive Example Jwere measured according to the procedures described hereinabove. The barsoaps were then subjected to environment stresses in an incubator at 50°C. with 60% humidity and ambient condition for 12 days, after whichfinal ZPT contents were measured. The measurement results are asfollows:

TABLE XI ZPT (w/w %) ZPT (w/w %) Ambient storage 50° C./60% humidityResults 12 days 12 days Comparative Example I 0.20 (+/−0.01) 0.15(+/−0.01) Inventive Example J 0.20 (+/−0.01) 0.20 (+/−0.01)

The above examples demonstrated that ZPT in a bar soap compositioncontaining uncomplexed HNPO is less stable than in that contained ZPTand Zn—HNPO complex.

Example 5 Synergistic Anti-Microbial Activity

Five different bar soap samples 1-5 were prepared containing ingredientsas listed in Table V below. Specifically, Example 1 contained 0.5 wt %Zn—HPNO complex. Example 2 contained 0.5 wt % ZPT. Example 3 contained0.1 wt % ZPT with 0.1 wt % Zn—HPNO complex. Example 4 contained 0.25 wt% ZPT with 0.25 wt % Zn—HPNO. Example 5 contained 0.5 wt % ZPT with 0.5wt % Zn—HPNO.

TABLE XII Comparative Comparative Inventive Inventive InventiveIngredients (wt %) Example 1 Example 2 Example 3 Example 4 Example 5Soap Noodle* 78.40 79.00 79.13 78.87 77.36 ZPT (48%) — 1.04 0.21 0.521.04 Zn-HPNO complex* 0.91 — 0.18 0.46 0.91 (active 55%) TiO2 0.50 0.500.50 0.50 0.50 Brightner 49 0.02 0.02 0.02 0.02 0.02 Starch 17.00 17.0017.00 17.00 17.00 Perfume 1.00 1.00 1.00 1.00 1.00 Pentaerythrityltetra- 0.03 0.03 0.03 0.03 0.03 di-t-butyl hydroxyhydrocinnamate DIWater Q.S. Q.S. Q.S. Q.S. Q.S. *Same as that described in Table IV.

The pigskin Residual Efficacy Test (RET) test was conducted for theComparative Examples 1-2 and the Inventive Examples 3-5, as follows:

First, pigskins were obtained from a local source. Pig hides wereshaved, washed with soap, rinsed, cut into usable pieces, and thensterilized by irradiation. Sterilized pigskin pieces were stored at −80°C. until used.

An overnight bacterial culture of S. aureus (ATCC #27217) was preparedon the day prior to performing the pigskin RET method. Specifically, onebacteria colony of S. aureus (ATCC #27217) from a streak plate was usedto inoculate into a vented flask containing 50 mL of Trypitic Soy Broth(TSB) and incubated at 33° C. for 18±2 hr with shaking at 200 rpm. Onthe day of the study, the overnight culture was diluted 1:20 in TSB, and10 μL (10⁶-10⁷ cfu) of the diluted culture was used for inoculatingpigskin slices that had already been washed by the bar soaps asdescribed above.

Frozen pigskins were thawed to room temperature for 60-90 minutes, andthen cut into 5×10 cm² pieces for bar soap washing. Pigskin pieces wereaffixed to a solid support using clamps to hold the skin into a fixedposition, then rinsed for 15 seconds under the tap with a water flow of4 L/min and a temperature ranging from 31° C. to 34° C. A bar soap testsample was subsequently wetted for 5 seconds with tap water and thenused to wash the pigskin directly for 15 seconds by rubbing the bar soapagainst the skin. Subsequently, the bar soap was put aside, and thepigskin was lathered further with a gloved hand for 45 seconds. Thesoap-washed pigskin was then rinsed again with tap water. The watercontacted the top-middle part of the skin held in a horizontal positionfor 15 seconds, then dried with a sterile kimwipe by gentle touching,followed by further air-drying.

The air-dried pigskin pieces were segmented using a sterile razor blade.A 2.5×10 cm² strip from the bottom part of the pig skin furthest awayfrom where the rinse water stream contacted the pig skin was cut awayand then further segmented into 1.75×2.5 cm² slices for use in theassay. Triplicate pigskin slices were inoculated with 10 μL of theprepared 1:20 bacteria dilution stock and spread on the skin with asterile 1 μL inoculating loop. The inoculum was 10⁶-10⁷ cfu for eachtissue slice. The inoculum was allowed to dry on the tissue slides, andthe resulting tissues were incubated in a large covered petri plate for5 hours at 33° C., 60% RH. After the 5-hr incubation, tissue slices wereplaced into individual sterile 250 mL wide mouth bottles containing 50mL MLBT neutralizing buffer (Modified Letheen Broth+1% Tween-80) andvigorously agitated by shaking for 1 min. Serial dilutions were thenmade using MLBT and surviving bacteria were plated onto MLTA (ModifiedLetheen Agar+1% Tween-80) and quantified using a QCount instrument(Spiral Biotech). Data was subsequently analyzed and graphed usingGraphPad Prism v6.01 software (GraphPad Software Inc.).

FIG. 1 shows the bacteria reduction rates of Examples 1-5 against thegram-positive bacteria, Staphylococcus aureus (S. aureus), as measuredby the above-described pigskin RET test. It is clear from that thebacterial reduction rate of Example 5, which contained both ZPT andZn—HPNO complex at 0.5 wt %, is significantly greater than the sum ofbacterial reduction rates of Examples 1 and 2, each of which containedZPT or Zn—HPNO complex alone at the same concentration. In fact, thebacterial reduction rate of Example 4, which contained ZPT and Zn—HPNOcomplex at a much lower concentration of 0.25 wt %, is even greater thanthe sum of bacterial reduction rates of Samples 1 and 2 that containedhigher concentration (i.e., 0.5 wt %) of ZPT and Zn—HPNO separately.

Therefore, a synergistic antimicrobial effect was observed for personalcleansing compositions containing the combination of ZPT and Zn—HPNOcomplex, especially against gram-positive bacteria, such as S. aureus.

Example 6 Fractional Inhibitory Concentration (FIC) Test

Four different test agents, which included HPNO, Zn—HPNO, Octopirox, andZn-Octopirox, were tested in combination with ZPT using the checkerboardFractional Inhibitory Concentration (FIC) microtitration method againstthe gram-positive model bacteria, S. aureus. Specifically, each test wasrepeated three times with HPNO and Zn—HPNO complex in combination withZPT, while each test was performed once with Octopirox and Zn-Octopiroxin combination with ZPT. The EFIC indices were determined and averaged(Table XIII). Definitions of the activity were applied according to TheAmerican Society of Microbiology criteria for determining druginteractions.

Specifically, a 1:1000 S. aureus (ATCC #27212) bacteria inoculum wasprepared from a 50 ml culture in TSB broth which was incubated (18-24hr, 33° C.) the night prior to each study. Stock solutions for each testmaterial were prepared in sterile water. Using 8 well (columns) by 8well (rows) grid on a 96-well microtitre plate, 2× stocks (100 μL) oftest material #1 (HPNO, Zn—HPNO, Octipirox, or Zn-Octipirox) was addedto the columns of a 96-well plate with decreasing 2-fold dilutionsacross the plate. The final concentration range for Zn—HPNO was 1242.5ppm to 19.4 ppm for a total of seven dilutions. The final concentrationrange for HPNO was 2500 ppm to 39 ppm for a total of seven dilutions.The final concentration range for Octopirox was 760 ppm to 11.9 ppm fora total of seven dilutions. The final concentration range forZn-Octopirox was 55000 ppm to 859 ppm for a total of seven dilutions. Ineach case the final (8^(th)) column contained none of the beforementioned materials to provide a zero material column in the firstdimension on the plate. In the second dimension of the plate, 10× stocks(20 μL) of ZPT was added to the “rows” of the same 96-well plate withdecreasing 2-fold dilutions down the plate. The concentration range (25ppm to 0.39 ppm for 7 dilutions) of ZPT was tested with the final(8^(th)) row containing no ZPT. Finally 80 μL of the previouslydescribed 1:1000 diluted S. aureus stock was added to each well of thematrix to provide a final volume of 200 μL in each well. This matrixallows for each concentration dose of ZPT to be exposed to eachconcentration dose of the respective test materials in the presence tothe bacteria. The test plates were then incubated 22-24 h, 33° C., afterwhich growth (opaque wells) and no growth (clear wells) determinationsof each well were determined by visualization. Based on the growth orlack of growth in dosed wells, the ΣFIC indices were calculated todetermine synergism, partial synergism, indifference, or antagonismaccording to The American Society of Microbiology criteria fordetermining drug interactions. Averages of the ΣFIC indices with theStandard Error of the Mean (SEM) are shown in TABLE XIII below.

TABLE XIII Samples S. aureus ZPT + ZnHPNO 0.27 ± 0.02 ZPT + HPNO 1.25 ±0.38 ZPT + Zn-Octopirox 1 ZPT + Octopirox 2

Typically, a FIC test value of <0.5 represents a synergistic effectachieved by the combination of ZPT with the additional ingredient inreducing or removing the gram-positive bacteria S. aureus. A FIC testvalue of 0.5-0.99 represents an additive or partial synergy effect. AFIC test value of 1-4 indicates that no difference was observed bycombining ZPT with the additional ingredient. A FIC test value of >4represents an antagonistic effect.

Therefore, the above-provided FIC test results further confirmed thesynergistic anti-microbial effect achieved by combining ZPT with aZn-pyridine oxide compound of the present invention in reducing orremoving the gram-positive bacteria S. aureus, which was not observedwhen an uncomplexed pyridine oxide compound (e.g., HPNO or Octopiroxwithout Zn) was added into the solution containing ZPT.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Every document cited herein, including any cross referenced or relatedpatent or application and any patent application or patent to which thisapplication claims priority or benefit thereof, is hereby incorporatedherein by reference in its entirety unless expressly excluded orotherwise limited. The citation of any document is not an admission thatit is prior art with respect to any invention disclosed or claimedherein or that it alone, or in any combination with any other referenceor references, teaches, suggests or discloses any such invention.Further, to the extent that any meaning or definition of a term in thisdocument conflicts with any meaning or definition of the same term in adocument incorporated by reference, the meaning or definition assignedto that term in this document shall govern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A personal cleansing composition comprising: (a)from 0.01% to 5% by weight of zinc pyrithione (ZPT); (b) from 0.01% to10% by weight of particles of a metal-pyridine oxide complex; and (c)from 20% to 95% by weight of at least one surfactant, wherein saidpersonal cleansing composition has a pH value ranging from 9.9 to 10.7when dispersed in a 1 wt % aqueous solution.
 2. The personal cleansingcomposition of claim 1, wherein the metal in the metal-pyridine oxidecomplex is selected from the group consisting of iron, copper, and zinc.3. The personal cleansing composition of claim 2, wherein the metal iszinc.
 4. The personal cleansing composition of claim 3, comprising aZn-pyridine oxide complex which comprises a pyridine oxide compound thatis coordinately bound to zinc ions, and wherein the pyridine oxidecompound is selected from the group consisting of2-hydroxypyridine-N-oxide (HPNO), N-hydroxy-6-octyloxy-2(1H)-pyridone,ciclopirox olamine, piroctone olamine, and derivatives and combinationsthereof.
 5. The personal cleansing composition of claim 4, wherein themolar ratio of ZPT to the Zn-pyridine oxide complex ranges from 5:1 to1:10.
 6. The personal cleansing composition of claim 1, furthercomprising a reducing agent.
 7. The personal cleansing composition ofclaim 6, wherein the reducing agent is a sterically hindered phenol. 8.The personal cleansing composition of claim 6, wherein the reducingagent is pentaerythrityl tetra-di-t-butyl hydroxyhydrocinnamate.
 9. Thepersonal cleansing composition of claim 4, wherein the Zn-pyridine oxidecomplex comprises 2-hydroxypyridine-N-oxide (HPNO) coordinately bound tozinc ions, wherein the molar ratio of ZPT to the Zn-pyridine oxidecomplex ranges from 5:1 to 1:10, wherein the composition furthercomprises a reducing agent that is pentaerythrityl tetra-di-t-butylhydroxyhydrocinnamate.
 10. The personal cleansing composition of claim1, which is in the form of a bar soap.
 11. The personal cleansingcomposition of claim 1, wherein the surfactant comprises: (a) from 0% to95% fatty acid soap; (b) from 0% to 50% synthetic surfactant; or (c)mixtures thereof.
 12. A bar soap comprising from 0.01% to 5% of ZPT,from 0.01% to 10% of particles of a Zn-pyridine oxide complex, and from20% to 95% of at least one synthetic surfactant by total weight of thebar soap.
 13. A method for forming a bar soap, comprising the steps of:(a) forming a mixture that comprises from 0.01% to 5% of ZPT, from 0.01%to 10% of particles of a Zn-pyridine oxide complex, and from 20% to 95%of at least one surfactant by total weight of the mixture; and (b)shaping the mixture to form a bar soap.
 14. The method of claim 13,wherein the bar soap has a pH value ranging from 9.9 to 10.7 whendispersed in a 1 wt % aqueous solution.
 15. The method of claim 13,wherein the Zn-pyridine oxide complex comprises a pyridine oxidecompound that is coordinately bound to zinc ions, and wherein saidpyridine oxide compound is selected from the group consisting of2-hydroxypyridine-N-oxide (HPNO), N-hydroxy-6-octyloxy-2(1H)-pyridone,ciclopirox olamine, piroctone olamine, and derivatives and combinationsthereof.
 16. The method of claim 13, wherein the molar ratio of ZPT tothe Zn-pyridine oxide complex ranges from 5:1 to 1:10.
 17. The method ofclaim 13, wherein the particles of Zn-pyridine oxide complex arepre-formed by combining a pyridine oxide compound with zinc oxide or asoluble zinc salt and then mixed with ZPT and the surfactant.
 18. Themethod of claim 13, wherein the particles of Zn-pyridine oxide complexare formed in situ by directly combining a pyridine oxide compound, azinc source selected from zinc oxide or a soluble zinc salt, ZPT and thesurfactant.
 19. The method of claim 13, wherein the mixture furthercomprises a reducing agent comprising a sterically hindered phenol. 20.The method of claim 13, wherein the mixture further comprisespentaerythrityl tetra-di-t-butyl hydroxyhydrocinnamate in the amountranging from 0.001% to 5% by total weight of the mixture.